The present invention relates to a method of forming a needle for an auto-sampler of an analytical device such as a liquid chromatograph for analyzing liquid as an analytical subject.
In an auto-sampler, it is necessary to clean a needle after collecting a certain sample. The cleaning process is important in order to prevent a previous sample from mixing into a next sample (cross-contamination). The needle is typically made of stainless steel, i.e., an alloy consisting mainly of iron. Accordingly, iron is microscopically exposed on a surface of the needle, and a certain ingredient in a sample may preferably adhere to iron due to a chemical property of iron. For example, an alkaline substance easily adheres chemically due to a hydroxyl group thereof attracted to iron on a surface of stainless steel. Once an ingredient of a sample adheres chemically, it is difficult to remove the ingredient even through physical cleaning with a cleanser of organic solvent. A trace amount of the ingredient may adhere to a surface of the needle even after cleaning. Accordingly, it is possible that the ingredient mixes into a next sample when the next sample is collected, thereby causing cross-contamination.
In order to prevent the cross-contamination, the needle is coated with a layer of precious metal, synthetic resin, quartz, or the like, thereby preventing the chemical adsorption phenomenon (see Patent Document 1).
Patent Document 1; Japanese Patent Publication (Kokai) No. 2002-228668.
Even when the needle is coated with metal or resin for preventing the chemical adsorption phenomenon, it is possible that the needle has a rough surface depending on a process of metal plating or resin coating. As a result, small bumps and cavities may be formed on the surface of the needle. In this case, liquid may penetrate into a pleat of the bump or cavity and remain on the surface of the needle, thereby causing cross-contamination.
In view of the problems described above, an object of the present invention is to provide a method of forming a needle for an auto-sampler with a coated surface and capable of preventing cross-contamination.
Further objects and advantages of the invention will be apparent from the following description of the invention.